linux-kernel - Re: [PATCH]mm:Correctly update number of rotated pages on active list.

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Message-ID: <20151203105948.GE9264@dhcp22.suse.cz>
Date:	Thu, 3 Dec 2015 11:59:48 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	"Pradeep Goswami (Pradeep Kumar Goswami)" 
	<Pradeep.Goswami@...eadtrum.com>
Cc:	"rebecca@...roid.com" <rebecca@...roid.com>,
	"vdavydov@...allels.com" <vdavydov@...allels.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"vbabka@...e.cz" <vbabka@...e.cz>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"sanjeev.yadav@...eatrum.com" <sanjeev.yadav@...eatrum.com>
Subject: Re: [PATCH]mm:Correctly update number of rotated pages on active
 list.

On Thu 03-12-15 10:08:11, Pradeep Goswami (Pradeep Kumar Goswami) wrote:
> This patch corrects the number of pages which are rotated on active list.
> The counter for rotated pages effects the number of pages
> to be scanned on active pages list in  low memory situations.

Why this should be changed?

This seems to be deliberate:
        /*
         * Count referenced pages from currently used mappings as rotated,
         * even though only some of them are actually re-activated.  This
         * helps balance scan pressure between file and anonymous pages in
         * get_scan_count.
         */
        reclaim_stat->recent_rotated[file] += nr_rotated;

What kind of problem are you trying to fix?

> 
> Signed-off-by: Pradeep Goswami <pradeep.goswami@...edtrum.com>
> Cc: Rebecca Schultz Zavin <rebecca@...roid.com>
> Cc: Vladimir Davydov <vdavydov@...allels.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
> --- a/mm/vmscan.c       2015-11-18 20:55:38.208838142 +0800
> +++ b/mm/vmscan.c       2015-11-19 14:37:31.189838998 +0800
> @@ -1806,7 +1806,6 @@ static void shrink_active_list(unsigned
>  
>                 if (page_referenced(page, 0, sc->target_mem_cgroup,
>                                     &vm_flags)) {
> -                       nr_rotated += hpage_nr_pages(page);
>                         /*  
>                          * Identify referenced, file-backed active pages and 
>                          * give them one more trip around the active list. So
> @@ -1818,6 +1817,7 @@ static void shrink_active_list(unsigned
>                          */  
>                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
>                                 list_add(&page->lru, &l_active);
> +                               nr_rotated += hpage_nr_pages(page);
>                                 continue;
>                         }   
>                 }   
> 
> Thanks,
> Pradeep.
> --
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-- 
Michal Hocko
SUSE Labs
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